Automatic regulation of rail flaw detection sensitivity



AUTOMATIC RGILATION 0F' RAIL FLAW DETECTION SENSTIVITY Filed May 18, 1948 Feb. 6, 1951 D E FARMER 2,540,870

/9 275/2? 20 bf2@ f'/ l/9 Patented Feb. 6, 1951 UNITED AUTOMATIC REGULATION OF RAIL FLAW DETECTION SENSITIVITY Daniel E. Farmer, Danbury, Conn., assignor to Sperry Products, Inc., Hoboken, N. J., a corporation of New York Application May 18, 1948, Serial No. 27,645

(Cl. F75- 183) Claims.

This invention relates t0 rail aw detector mechanisms of the type now employed on Sperry rail flaw detector cars. These cars run along the railroad tracks and pass current continuously through the rails between spaced contact brushes to set up an electromagnetic field surrounding the rail. Flaws in the rail caused by issures are discovered by reason of the fact that they set up non-uniform regions in the said electromagnetic eld. Such non-uniformities are detected by means of opposed induction coils maintained at a constant distance above the railhead, The coils normally cut a constant number of lines of force but on encountering a region of flaw, they cut a diierent number of lines of force to generate an E. M. F. which, aftenbeing suitably amplied, may be caused to operate indicating means. Such indicating means may take the form of a relay which, when energized with a predetermined voltage output from the amplifier is caused to attract its armature in the form of a recording pen operating on a moving chart which is geared to the wheels to move in predetermined relation to the movement or the car. In addition, the output of said relay, or of a separate re lay, may be caused to actuate a paint gun to discharge paint on the rail in the regio-n of tlaw.

As stated above, the indicator relay was set to operate in response to a predetermined voltage output from the amplifier. However, the output from the amplier was subject to several variations not caused by the aw in the rail. One of these variations Was due to the variation in the amplifier sensitivity and this required that the amplier Ibe calibrated at frequent intervals.

Another variation in the amplier output was the result of variation in ampliiier input caused by the variation in running speed of the car, since the voltage induced in the induction coils which detect the fissure is a function of the speed with which said coils (carried by the car) cut the lines of flux. A third variation in the amplier output was also due to a variation in amplier input resulting from variation in the amount of current passed through the rail for the purpose of setting up the electromagnetic flux. Since the voltage induced in the detector coils is a product of the speed of the coils and the number of lines of force which the coils cut, it can be seen that variation in the amount of current in the rail resulted in a variation in the number of lines of force which the coils would cut.

It is one of the principal objects of this invention, therefore, to provide a method and means whereby the effect on the indicator relay of all of 2 the above-mentioned variations will be minimized.

Still another variation in actuation of the naw indicating means occurred in the indicator relay itself, which, by reason of its characteristics, as in the case of a Thyratron, required more or less voltage to actuate the indicator. Therefore, an induced voltage of a certain magnitude which might be suiiicient to operate the indicator relay at one time would not be sufficient to operate the indicator if the relays characteristic had changed so as to require a larger tripping voltage. Thus, certain small ssures which, under certain circumstances would indicate, would, under the condition of a different relay characteristic, not be indicated and would therefore be missed. It is, therefore, another object of this invention to provide a method and means whereby the variations in relay characteristics will have a greatly reduced effect on the aw indicating means than,

was heretofore the case.

Further objects and advantages of this invention will become apparent in the following detailed description thereof.

In the accompanying drawings,

Fig. 1 is a side view of a portion of a Sperry rail fissure detector car having my invention applied thereto.

Fig. 2 is a view consisting mainly of wiring diagram illustrating the principle of this invention.

Referring to Fig. 1 of the drawings, there are shown the parts of a standard Sperry rail iissure detector car which includes a car body I0, operating along the rails R. Fissure detection is accomplished by passing current through each rail from a generator G within the car body supplying current to spaced current brushes Il and l2 supported upon the current brush carriage I3 which when in lowered or effective position is adapted to ride upon the rail by means such as wheels I5. The current brush carriage I3 is normally held in elevated or ineiective position by means of springs (not shown) and cables I8, but when it is desired to lower said carriage, I'iuid pressure such as compressed air is supplied to the cylinders il to force out pistons I8 which are pivotally connected at I9 to the current brush carriage I3. The current passed thro-ugh the rail by way of spaced brushes II and I 2 will establish an electromagnetic eld surrounding the rail and this field will be uniform except in the region of flaw where it will be distorted. Such distortions of the electromagnetic eld are detected by a flaw responsive mechanism which may take riding onthe railonpmeans suchaswheelsrl, to. move independently of" carriage leso that said`r carriage 24 may at all times maintain parallelism with the rail surface regardless of irregularitiesr thereof.

The iiaw responsive mechanism maar.V include-A a plurality of pairs of coils, two such pairs` 2d and 2i being shown in the present instance.-y

Each pair of coils is connected-inseriesand'ope positely Wound so that variations in iiux, such as variations in the current supplyoriequalvaria-V tions in the distance of the coils above the rail, will affect both equally and oppositely. @n en- Vtering a region of flaw, however, rst one and their= the other'otthee coils of; each pair will" cut.V

a different number of lines of force from.A that` which'. was previously: cut. ands thus: therev will-be kgeneraal-red. an M.v This, E; M. F.1maysbe. amplified. byzan-.amplier 211i, and'vvhen': the output. of. said ampliiier exceeds` a predetermined voltage', it will energize; relay 3@l to. cause it to attract itsarmature 3l; which carries a pen- B operating cna movingchart gearedk to; the car'wheel., TheipeniEfwill; thus make notch. inztheeothenwise straight line which it drawsand said: notch. will, indicate` thel region of Flaw.

From. the.l above, description. of. the standard mechanism: of` a.Sperry rail flaw detecten car,

it quite. apparent: that: .the relay 36 requires acertaintripping voltage tooperate pen P and.v it isffurtherapparent thatthis tripping voltage maybe aiiectedbyrany onel of theiour: factors mentionedfin: the-f introduction hereto, i. e; (l)A variationslin thesensitivity of'vainpliiier Zi?, (2) the speed oi the car, (3) thefcurrentin.theoifail, andhence. the number ofV lines: of force;v and (4f). variationsin thefisensitiv-ityoff therelay; My invention provides means:Y fon minimizing thel eiect of all these variations; aszwillibedescribed hereinafter:-

The: relay `3!! willi` attract its: ar-matureor penI bya suitable amplier such as amplifier 2l.

I2 and variations in the speed of the car. In orderv to minimize the effect on the indicator of variations in the amount of current in the rail and variations in the speed of the car, I provide the following method and means.

Heretofore the net voltage generated by a pair oielectrically Opposed detector coils; suohfas coils 2i); on entering aregionof= ila-w was applied to the actuationrof the relay 3i) after being amplified The relay Was-, set. so that the voltage output from amplifier` 211.1 in response to the detector coils passing over the minimum sized fissure to be detected-(say 5%1); with full energization of the railand maximumtesting speed of the car would be; just sufficient to actuate the pen 3l. So rfl:iat,f.or-example,4 if the voltage output under the aforesaid conditions was 1 volt, the relay was set'sothat it would require at least 1 volt to actuate the pen. If, however, the car speed diminished orK theifamount;v or: currentr im thezxrail dimirs-hed then it: is: obvioua that a-smalleri amount. oi'fvoltageicutput would be obtainedirom;

amplien 2 l' in response, to .the same v sized. fissure;` and therefore'v theepen would=4 not.: bes aci'f-uatgediA Under; these` conditions; it; .vouldzrequire; a. much, larger sizedssure'toactuatefthegpen; andthere.-

fore smaller sized fissures which; would loe-deeV testedv with full; energizationtand.; maminmm:carV speedI would not. be,` detecterli'with dirninislied.

energization andcar speed... Fonz example-i as,-

sume that the voltage.generated;by.` coils.

been, cut in. half vduerto; reduced: can speedy: re:

Y operativer output rromamplier 2711-:

3| against the action of restraining springy 321' when: outputzrom ampliliery Zl'l exceeds a pre-V deter-mined minimum Voltage.WV This minimumvoltage is the voltage represented by the netV M; En generated'bytheesearching coils when Vpassing over the smallest sizesA defectwliioh it is desired; to' detect, when. amplified-@by amplifier-2l at aipredeterrnined sensitivity. Thus,4 if 'thev arn-Y plier sensitivity slrlould" drift lower,k or'- if the currentthrough the rail' should' drop, or if Vthe `fore the output voltage generated 'when the coils pass a minimum defect would not be indicated: The iirst.A ofthese variations-` can be I elinfiinated'l by making amplier 2jr-o the constant gain type which isi based upon the principle of degener ative {ecdl-'hack from'Y the output of the ampliierto its inizgut;` Such ampliiiers are well: knownand' the details thereof; therefore; described.

Y The other two variations in amplieroutput in response to'fthecoils passing over a defect` areY duetc variations `in thev amount of'current passedI need-notte.

Y [Not using differentiall Enom theabovevtablee it.- isv apparent that' irl the relay isset; to operatealz llvolt ai: 51%r rl'ssure vvillzibe,detected with,k fullener-gization andi maXiJ-Q mum can speed;Y but theasmal'lesti-ssure whichV will' be'1detected-.when the arnpliierfoutput-is-cut-Y inhalris a 10% fissure, andallifissures'osmaller:J

' size than 10%Y willfznot; be detected;

By/.tlie` arrangement shown? in Fig; 2f I pro-VA duce a iar-` moreV stable systemwhichz-will beV only slightly affected by- Vlargevariations-` inrail energization--Yandi` car' .speeda Forl this'pur-pose- Y I operate not upon; the principle of utilizing-theAV say( 5%,` and with fullA Y energiz'ati'on of' therailfV and-maximum' car speed' the output from anr- Y plifier-Z is 1` volt, I'may'oppose this o utpu't'by" Y a voltage on the order-voi .9.vo'lt.generatedliy` coil l2^ rotatedfirfr prornixity`A to lthe rail' by means.

I n cfa;Vdriving'connection' rfromthercar*wheel" 'cthroughtherailbetween'current-brushes HY andy;v liso'that'theamouut OFVQltageinduced in coil' 42 will be a function of the sped of the car and the energization of the rail. The number o f turns of coil 42 is such as to generate a voltageon the order of .9 volt when the rail is receiving full current nergization and the car is traveling at maximum operating speed. This voltage may be taken off a oommutator 44 on driving connection 43 by means of brushes 45. Under these conditions when coils 2D pass over a minimum i'issure of 5% there will be generated adiferential voltage in the rectiiier or diode 40 of le volt, the voltage generated by coil 42 being applied to one element 4| of the diode and the voltage output of amplifier 21 being applied to the other element 5| of the diode. Normally there is voltage on plate 4|, but only when a fissure is encountered is there voltage on element 5|, and only when the voltage on element 5| exceeds the voltage on element 4| will current pass to the relay 30. The voltage Voutput of amplier 21 will generate a voltage in excess of the voltage on plate 4| whenthe coils 2G encounter a fissure of minimum size or greater, in the example cited, 5%. The voltage generated by coil 42 is not responsive to 'fissures because the voltage is passed through a lter 46 having a long time constant which, therefore, does not respond to the short-period variations characteristic of iissures. Only the coils 2B, therefore. will respond to a iissure.

By utilizing only the differential output from diode 4l] I may employ a very small differential, such as .1 volt. It is true that should the output of amplier 21 and coil 42 be reduced to half through reduced energization of the rail or through reduced car speed, the .1 volt differential will be reduced to .05 volt differential. While the percentage reduction in diierential is high 50%), the amount of voltage reduction is small. The relay 30 can be made so that pen 3| is actuated in response to .1 volt differential so that a 5% fissure will be the smallest to be indicated. It will be seen that if the differential is reduced to .05 volt the pen 3| will not be energized. However, it is necessary to raise the voltage generated by coils 20 through the amplifier 2'! by only .05 volt in order to actuate the pen 3|. This does not require that the coils 2U rpass over a iissure twice the size of the minimum, i. e., a. iissure, but only that it pass over a iissure slightly larger than 5% and less than 6%. This becomes apparent from the following table:

[Using differential] With full energization and maximum speed to Wtdrddtoenzm yield maximum output out gt f amyuer 27 Per cent of amplifier 27 p p fissure Out ut Output Output Output of gv of 46 Dm' of of 46 Dui 5 1. 0 9 1 5 45 05 G 1. 2 9 3 6 45 15 7 1. 4 9 5 i 7 45 25 8 l. 6 9 7 8 45 35 9 1. 8 9 9 9 45 45 10 2.0 .9 1.() 1.0 .45 .55

From the above table it becomes apparent that a fissure oi less than 6% will provide a differential output in excess of the .1 volt necessary to actuate the pen 3|. Thus, whereas in the case of the arrangement heretofore used where the absolute voltage generated by coils was utiilzed without opposing a differential voltage, it required a fissure twice the size to actuate the indicator if the reduced rail energization and car speed cut the induced voltage in half, with the present arrangement, using a differential voltage, and a more sensitive relay, it is only necessary to encounter a iissure less than 1% larger than the minimum in order to actuate said indicator.

Applioants arrangement also will taire care of variations in relay characteristics which occur, for example, when the type of relay employed is a Thyratron. Such variation in relay characteristics may mean that instead of operating the pen in response to .1 differential, the relay may not operate until .2 volt is applied thereto. In this case, it will be seen from the above table that a ssure of less than 6 size would yield a differ ential in excess of .2 Volt, and therefore all :dssures of 6% or more in size would be indicated. In the system heretofore used without passing a differential voltage it will be seen that if the voltage necessary to operate the relay rose `from 1.0 volt to 2.0 volts, i. e., the voltage necessary to operate the relay was doubled, the smallest iis sure that would come through would be a 10% fissure and all fissures of smaller size would not be indicated.

Having a described my invention, what I claim and desire to secure by Letters Patent is:

l. In a rail. flaw detector car having means :for energizing the rail with flux, means responsive to said dus and adapted to generate a voltage which is a function of the speed of the car, the iiux sur rounding the rail and the short-period flux distortion caused by a rail defect, a second means` responsive to flux and adapted to generate a voltage which is a function 'of the speed of thel car, the ilux surrounding the rail and the short- Aeriod iiux distortion caused by a defect, means for filtering out said short-period iiux distortion voltages generated by said second responsive means, means for opposing the voltage generated by said f rst responsive means against the voltage delivered by said second responsive means` after ltering, indicating means, and means for actuating the indicating means in response to the diiierential of said voltages.

2. In a rail flaw detector car having means or energizing the rail with flux, inductive means responsive to said ux and adapted to generate a voltage which is a function of the of the car, the iiux surrounding the rail and the short period flux distortion caused by a rail defect, a second inductive means responsive to iiux and adapted to generate a voltage which .is a function of the speed of the oar, the flux surrounding the rail and the short-period flux distortion caused by a defect, means for ltering out said short-period fiux distortion voltages generated by said second responsive means, means for opposing the voltage generated by 'first ductive means against the voltage delivered by id second inductive means after ltering, indicating means, and means for actuating the indicating means in response to diierential of voltages.

3. In a. rail flaw detector car having for energizing the rail with flux, means responsive to flux and adapted to generate a voltage which is a function of the speed of the car, the iiux surrounding the rail and the flux distortion caused .by a rail defect, a second means responsive to Jflux and adapted to deliver a voltage which is a function of the speed oi the car and the ux surrounding the rail, but not of the distortion caused by a defect, means for opposing the voltage generated by said rst responsive means against the voltage delivered by said second ree` 10. In a rail flaw detector car having means for energizing the rail with flux, a pair of equal opposed induction coils arranged in tandem along the rail, each coil generating a voltage which is a function of the speed of the car, the ux surrounding the rail and the flux distortion caused by a rail defect, whereby a net voltage will be generated when a rail defect is encountered, a constant gain amplier for amplifying said net voltage, a rotatable induction coil positioned in the flux field surrounding the rail, means for rotating said coil as a function of the car speed whereby said rotatable coil will generate a voltage which is a function of the speed of the car, the flux surrounding the rail and the iiux distortion caused by a rail defect, said ux distortion caused by a rail defect being adapted to generate short-period voltages, means for filtering out said short-period voltages, means for opposing the output of said amplifier against the voltage generated by said rotatable coil after passing through the filter, whereby a differential I Y '1' voltage is obtained, indicating means, and means for actuating the indicating means in response to said diii'erential voltage, said last named means comprising a diode, means for applying to the diode the voltage generated by the rotatable coil after passing through the filter, in a direction to render the diode non-conducting, and means for applying to the diode the output of said amplifier, in a direction to render the diode conducting.

DANIEL E. FARMER.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date Re. 18,555 Sperry Aug. 2, 1932 1,954,975 Zuschlag Apr. 17, 1934 2,228,294 Wurzbach Jan. 14, 1941 2,290,330 Irwin July 21, 1942 

